I remember a few news reports about “Nuclear Winter” causing a global cooling effect due to large amounts of firestorms or a war that used a “small” number of nuclear weapons. The nuclear weapons were hypothesized to inject large amounts of carbon dust into the atmosphere causing a volcano-like effect of cooling the atmosphere for a few decades. However, creating a real-world test of this theory had major obstacles. One problem was the need for insane world leaders who wanted a global nuclear war.
Of course, Mutual Assured Destruction (MAD: the acronym is a great description) policy in effect then guaranteed almost nobody would be left alive after such a war. Nobody would be around to observe the effects … or care about the effects.
I think I remember commercials for a television comedy about the aftermath of a nuclear war: it was called “Oops”.
This could be a source of “global cooling” stories.